Bruh you only played the polyamorous route and you're mad they were hooking up with other people? Not to mention Nika doesn't sleep with Vincent at all. It's just Maxim, and they are very broken up by the end of the route. As someone who has actually played all of the routes, Maxim and Vincent are in a fwb relationship in all of them, sure, but they separate in the routes where they're the LI to commit to MC (and Nika, in Maxim's case). The other LIs don't have any other serious romantic relationships. You're certainly not getting "cucked" in any of them.
Bruh, since when is polyamory just hooking up with random people? From what I understand, polyamory is about having multiple consensual relationships with people you actually love and care about, not just sleeping around. And from what I saw, neither Maxim nor Nika really seemed to care about Vincent or the other NPCs they were with when I played. I knew Maxim and Nika would be together with the MC, but I didn’t expect Victor and other NPCs to also be part of it in that way. Honestly, if I had known they were sleeping with others like that, I wouldn’t have bought the game at all. And even though I played it a while ago, I could swear Nika slept with Vincent especially since on the Last Call DLC page there’s literally a scene showing them having sex, so I’m not sure what your point is. But that’s just my opinion and experience, and I’m not going to argue with random people on the internet over a porn game.